Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $119.73   3.859%   $124.3504   $124.35   $124.35   $124.40  
  Purchase #2 $202.93   5.733%   $214.564   $214.56   $214.55   $214.60  
  Purchase #3 $59.88   13.688%   $68.0764   $68.08   $68.10   $68.10  
  Purchase #4 $190.84   5.149%   $200.6664   $200.67   $200.65   $200.70  
  Purchase #5 $27.36   8.533%   $29.6946   $29.69   $29.70   $29.70  
  Purchase #6 $108.89   13.640%   $123.7426   $123.74   $123.75   $123.70  
  Purchase #7 $236.65   4.596%   $247.5264   $247.53   $247.55   $247.50  
  7 purchase totals = $946.28       $1,008.6208   $1,008.62   $1,008.65   $1,008.70